Abstract: Agricultural fan control system for controlling operation of fan in an agricultural installation including a thermostat temperature control, a manual constant speed adjustment temperature control, and an automatic variable fan speed with a minimum temperature setting. The control system is fully enclosed in a dustproof, waterproof box with a spring-loaded cover for use in a barn. The sensor unit can be remote from the control unit, and accounts for a seven-degree fahrenheit temperature rise on modulating setting from minimum to maximum c.f.m. Voltage curve of the electrical system is inverted and slower so that there is a slower fan speed increase on the first five degrees than on the last two degrees temperature-wise. The system includes a minimum setting allowing for a constant minimum air movement while including a manual setting for maintaining constant maximum air movement. The c.f.m. to heat requirements is adjusted accordingly between 45.degree.-110.degree. F.